Collimation of atomic beams by resonant laser radiation pressure

The application of the resonant light pressure created by an axially symmetrical light field for collimating atomic beams has been considered. As an example, consideration is given to the possibility of collimating an atomic beam by the light field produced by the reflection of a plane wave from the internal surface of a metal cone. It has been shown that the radiation pressure can reduce the atomic-beam transverse velocities to the value of the order of 100 cm/s which corresponds to effective temperature of about 10^–3 K. A method for producing collimated beams of cold atoms based on simultaneous deceleration and collimation of atomic beams by resonant laser radiation pressure is proposed.     

Periodically dressed Bose-Einstein condensate: a superfluid with an anisotropic and variable critical velocity

We consider a two-component atomic gas illumined by two intersecting laser beams which induce Raman coupling between the components. This spatially periodic coupling modifies the dispersion relation of the gas. Properties of a Bose-Einstein condensate of such a gas are strongly affected by this modification. Using the quasiparticle excitation spectrum derived from a Bogoliubov transformation, the Landau critical velocity is found to be anisotropic and can be widely tuned by varying properties of the dressing laser beams.     

Intense source of cold cesium atoms based on a two-dimensional magneto–optical trap with independent axial cooling and pushing

We report our studies on an intense source of cold cesium atoms based on a two-dimensional(2D) magneto–optical trap(MOT) with independent axial cooling and pushing.The new-designed source,proposed as 2D-HP MOT,uses hollow laser beams for axial cooling and a thin pushing laser beam to extract a cold atomic beam.With the independent pushing beam,the atomic flux can be substantially optimized.The total atomic flux maximum obtained in the 2D-HP MOT is4.02 × 1010atoms/s,increased by 60 percent compared to the traditional 2D+MOT in our experiment.Moreover,with the pushing power 10 μW and detuning 0Γ,the 2D-HP MOT can generate a rather intense atomic beam with the concomitant light shift suppressed by a factor of 20.The axial velocity distribution of the cold cesium beams centers at 6.8 m/s with an FMHW of about 2.8 m/s.The dependences of the atomic flux on the pushing power and detuning are studied in detail.The experimental results are in good agreement with the theoretical model.     

Loading of a krypton magneto-optical trap with two hollow laser beams in a Zeeman slower

A significant enhancement in the number of cold atoms in an atomic-beam-loaded magneto-optical trap (MOT) for metastable krypton atoms is observed when hollow laser beams are used in a Zeeman slower instead of a Gaussian laser beam. In the Zeeman slower setup, a combination of two hollow laser beams, i.e., a variable-diameter hollow beam generated using a pair of axicon lenses superimposed on a fixed-diameter hollow beam, has been used to reduce the longitudinal velocity of the atoms in the atomic beam below the capture speed of the MOT. The observed enhancement in the number of atoms in the MOT is attributed to reduced destruction of the atom cloud in the MOT and increased cooling of the off-axis atoms in the atomic beam, resulting from the use of hollow beams in the Zeeman slower.     

Intense stationary flow of cold atoms formed by laser deceleration of atomic beam

Applying an optimum configuration of atomic and laser beams, a powerful two-frequency laser and restriction of velocity diffusion permitted us to obtain an intense stationary flow of atoms with an effective temperature down to 1 K. The decelerated atomic beam intensity exceeds that of the initial atomic beam by more than 3 x 10³.     

Photonic band gap of three dimensional magnetized photonic crystal with Voigt configuration

We study Bessel beams of two-level atoms that are driven by a linearly polarized laser field. Starting from the Schrödinger equation, we determine the states of two-level atoms in a plane-wave field respecting propagation directions both of the atom and the field. For such laser-driven two-level atoms, we construct Bessel beams beyond the typical paraxial approximation. We show that the probability density of these atomic beams obtains a non-trivial, Bessel-squared-type behavior and can be tuned under the special choice of the atom and laser parameters, such as the nuclear charge, atom velocity, laser frequency, and propagation geometry of the atom and laser beams. Moreover, we spatially and temporally characterize the beam of hydrogen and selected (neutral) alkali-metal atoms that carry non-zero orbital angular momentum (OAM). The proposed spatiotemporal Bessel states (i) are able to describe, in principle, twisted states of any two-level system which is driven by the radiation field and (ii) have potential applications in atomic and nuclear processes as well as in quantum communication.     

Non-equilibrium behavior on pulsed laser evaporated surfaces

Absorption of intense pulsed laser optical fields by metallic surfaces generates dense neutral atomic beams with high average translational energies. Mechanisms explaining this behavior are based on an equilibrium model invoking high temperatures and pressures. We have made experimental observations on yttrium and uranium atomic beams produced from laser evaporated targets which suggest an alternative mechanism involving a non-equilibrium process.     

Eu同位素浓缩的实验研究

极化原子束有许多重要的应用，如用来研究原子散射过程、制备极化核、检验宇称守恒性、研究表面特性以及应用于同位素的浓缩过程。本文主要描述通过磁偏转极化原子束的方法对Eu元素进行同位素浓缩实验，结合Eu原子特有的能级结构，分析了原子束的极化原理，描述了原子束极化和同位素浓缩的实验装置。用具有特定频率和偏振的激光对^153Eu进行选择性光抽运，分别得到正、负极化原子束，正、负极化原子束，正、负极化后的原子束穿过六极偏转磁铁后分别被聚焦和发散，最后用热丝探测器控制，得到了清晰的Eu原子的浓缩信号，当各参数为最佳状态时，仅用一台激光器对^153Eu进行抽运极化，其浓缩效率可达4％。     

Five-beam magneto-optical trap and optical molasses

We have operated a magneto-optical trap and optical molasses for the laser cooling of cesium atoms on the basis of a five-beam laser configuration. For the magneto-optical trap two laser beams counterpropagate along the axis of a quadrupole trap and the remaining three beams propagate in the orthogonal plane at 120° to each other. The same optical configuration was used for the optical molasses. We have tested the efficiency in atom collection and the temperatures reached in both cooling processes. In comparison to previous results on a six-beam configuration, a lower number of atoms is collected, while comparable densities are realized. The atomic temperatures have been measured through a delayed shadow-image technique, where one of the running-wave cooling beams produces an absorptive image of the atoms on a camera. Received: 14 January 1999 / revised version: 23 June 1999 / Published online: 8 September 1999     

One-off writing of multimicrogratings on glass by two interfered femtosecond laser pulses

Multimicrogratings are one-off written on silicate glass by two interfered femtosecond pulsed laser beams with the aid of a mask. The period and depth of the multimicrogratings are revealed by optical microscopy and atomic force microscopy. The depth is dependent on both the colliding angle between the two interfered laser beams and the laser pulse energy, but the period relies on the colliding angle only. We also observe a series of grooves formed at the middle of each bulge of the multimicrogratings and attribute it to the higher-order modulation arising from second-harmonic generation of the femtosecond laser pulse during the one-off writing processes.     

Laser cooling of antihydrogen

We present a short review of the essential techniques of cooling free atoms by resonant laser radiation. The different contributions to the light forces are explained and their application to the problem of damping the thermal motion of free atoms is described. Due to quantum mechanical fluctuations of the light force there exists a limit temperature for a given atomic transition. Deceleration of atomic beams by the radiation pressure demands techniques to maintain the resonance condition while the Doppler shift of the decelerated atom is rapidly changing. Radiation forces may serve to compress and deflect slow atomic beams as well as to trap cold atoms. The possible use of pulsed laser radiation is discussed.     

Propagation of laser array beams in a turbulent atmosphere

The propagation of phase-locked and non-phase-locked laser array beams of radial and rectangular symmetries in a turbulent atmosphere are investigated based on the extended Huygens–Fresnel integral. The beamlet used in our paper for constructing the laser array beams is of elliptical Gaussian mode. Analytical formulae for the average irradiance of phase-locked and non-phase-locked radial and rectangular laser array beams are derived through vector integration and tensor operation. The irradiance properties of these laser array beams in a turbulent atmosphere are studied numerically. It is found that both phase-locked and non-phase-locked radial and rectangular laser array beams eventually become circular Gaussian beams in a turbulent atmosphere, which is much different from their propagation properties in free space. The propagation properties are closely related to the parameters of laser array beams and the structure constant of the turbulent atmosphere. PACS 42.25.Bs; 41.85.Ew; 42.68.Ay     

The Kapitza-Dirac effect

The development of laser cooling has an important impact on many aspects of atomic physics and quantum optics. The efforts to understand the various types of force exerted on atoms by laser light have led to some interesting physics and it is now possible for extremely cold clouds of atoms to be produced, which can be confined in atom traps or formed into very monoenergetic atomic beams.

There are many new possibilities to explore in this ultra-cold regime where quantum effects are significant, in addition to the potential for great improvements in precision measurements made by r.f. and laser spectroscopy.     

Laser based accelerator for ultracold atoms

We present our first results on our implementation of a laser based accelerator for ultracold atoms. Atoms cooled to a temperature of 420 nK are confined and accelerated by means of laser tweezer beams, and the atomic scattering is directly observed in laser absorption imaging. The optical collider has been characterized using 87Rb atoms in the |F=2, m(F)=2] state, but the scheme is not restricted to atoms in any particular magnetic substates and can readily be extended to other atomic species as well.     

激光冷却获得高亮度的亚稳态惰性气体原子束和原子阱

高强度的亚稳态惰性原子束流在原子分子物理实验研究中具有广泛的应用.使用射频电离方法和激光横向冷却技术制备了高强度的亚稳态氪原子束流,并使用数值模拟方法对横向冷却激光场中的原子径迹进行了分析.通过激光诱导荧光光谱方法测量原子束的束流特性,结果显示,横向冷却后在束流源下游230 cm处的原子束流强度达1.6atoms/(s*sr),束流强度提高了两个量级.利用这种高强度原子束流,我们成功囚禁了1.3×10¹⁰个亚稳态⁸⁴Kr原子,同时冷原子装载速率达到了3.0×10¹¹atoms/s;并利用该装置成功地实现了高亮度的亚稳态氩原子束和原子阱. 关键词： 横向冷却 原子束 原子阱 惰性气体     

All-optical ion generation for ion trap loading

We have investigated the all-optical generation of ions by photo-ionisation of atoms generated by pulsed laser ablation. A direct comparison between a resistively heated oven source and pulsed laser ablation is reported. Pulsed laser ablation with 10 ns Nd:YAG laser pulses is shown to produce large calcium flux, corresponding to atomic beams produced with oven temperatures greater than 650 K. For an equivalent atomic flux, pulsed laser ablation is shown to produce a thermal load more than one order of magnitude smaller than the oven source. The atomic beam distributions obey Maxwell–Boltzmann statistics with most probable speeds corresponding to temperatures greater than 2200 K. Below a threshold pulse fluence between 280 mJ/cm² and 330 mJ/cm², the atomic beam is composed exclusively of ground-state atoms. For higher fluences ions and excited atoms are generated.     

Far-off resonance conditional phase-shifter using the ac Stark shift

We suggest a conditional phase-shifter that achieves a phase shift of π radians between two weak laser beams with a total energy density on the level of 1000 photons per atomic cross-section. The two laser beams interact through the simple nonlinear technique of ac Stark shifting the common ground state of a V-type system. We find that this switch can operate in the far-off resonance regime, with low absorption and high phase accumulation. Additionally, the bandwidth of this switch can be increased independently of the energy requirement.     

Coherent population trapping resonances in the problem of quantum filtering of light pulses

The conditions necessary to implement a single-photon pulse source using quantum filtering based on the coherent population trapping phenomenon in N-systems of atomic levels are determined. The dependences of dark resonance characteristics on laser field intensities are experimentally measured in Rb vapor. These dependences define optimum intensity ratios and pulse durations of used laser beams, at which the system can efficiently operate as a single-photon quantum filter.     

Fast-ion-beam laser probing of ion-source energy distributions and atomic structure

Collinear fast-ion-beam laser spectroscopy is a very high resolution probe for measuring ion-beam energy distributions and atomic structure parameters of interest in nuclear physics, atomic physics, and astrophysics. We have used offline 10-keV beams of atomic ions and a CW laser system to study the behavior of a Penning ion source and to measure hyperfine structure, isotope shifts, atomic lifetimes, spontaneous-emission branching fractions, oscillator strengths, and absolute wavelengths of a variety of atomic species from the lanthanide and transition-metal groups.     

Ionization Scheme Development at the ISOLDE RILIS

The resonance ionization laser ion source (RILIS) of the ISOLDE on-line isotope separation facility is based on the method of laser step-wise resonance ionization of atoms in a hot metal cavity. The atomic selectivity of the RILIS complements the mass selection process of the ISOLDE separator magnets to provide beams of a chosen isotope with greatly reduced isobaric contamination. Using a system of dye lasers pumped by copper vapour lasers, ion beams of 24 elements have been generated at ISOLDE with ionization efficiencies in the range of 0.5–15%. As part of the ongoing RILIS development off-line resonance ionization spectroscopy studies carried out in 2003 and 2004 have determined the optimal three-step ionization schemes for scandium, antimony, dysprosium and yttrium.